The invention relates to a compressor in a turbocharger.
German Published Patent Application No. 196 47 605 describes an exhaust-gas turbocharger for an internal combustion engine, the compressor of which has an axial inflow passage for supplying combustion air, which sucks in air via the rotating compressor impeller and conveys it via a radial diffuser at the compressor-impeller outlet edge into a helical passage. The charge air, which has been compressed to an elevated pressure, is usually discharged from the helical passage which radially surrounds the compressor impeller, via an outflow pipe, to the cylinder intake or a charge-air cooler, the outflow pipe, for space reasons, often being guided in the axial direction, so that a diversion of approximately 90xc2x0 is required between diffuser or helical passage and outflow pipe. This change in direction of the charge air which is to be removed may lead to pulsating flow delaminations and turbulence in the wall region of the outflow pipe, which leads to a throttling effect in the outflow pipe and has an adverse effect on the pump limit in the compressor characteristic diagram which limits the compressor operating range toward low mass flows passing through the compressor. The structural design of the outflow region of a compressor may therefore have an adverse effect on the working range.
A further adverse effect on the compressor working range may be caused by the pressure pulses which prevail in the induction line of the internal combustion engine, which have adverse effects on the compressor via the outflow region thereof and in particular may cause operation of the compressor in the vicinity of the pumping limit to deteriorate.
It is an object of the present invention to increase the working range of a compressor in a turbocharger by a simple arrangement.
The above and other beneficial objects of the present invention are achieved by providing a compressor in a turbocharger as described herein.
In total, the compressor outflow region has at least three sections of different configuration, which are in a defined, preset relationship with respect to one another. The compressor-impeller outlet edge is directly adjoined firstly by a connecting passage which, over the further flow path, opens out into a stabilizing chamber of widened cross-section. The connecting passage is in this case arranged with a lateral offset with respect to a longitudinal center axis of the stabilizing chamber, with the result that a swirling motion is imparted to the charge air which flows into the stabilizing chamber and has been compressed to a high charge pressure. Turbulence on entry to the stabilizing chamber is avoided by the widening in the cross-section of the stabilizing chamber compared to the connecting passage which supplies the air. The swirling flow may be generated or influenced by the offset of the axis with respect to the longitudinal center axis or the longitudinal center plane of the stabilizing chamber. To achieve sufficient swirling movement, a limit value may be predetermined which is to be exceeded for the ratio of the temporal offset between connecting passage and stabilizing chamber to the cross-section of flow of the connecting passage.
The stabilizing chamber is adjoined by an outflow passage, via which the compressed medium is discharged from the compressor and, in the case of an exhaust-gas turbocharger as a unit of an internal combustion engine, is fed to the cylinder inlet or an upstream charge-air cooler. The connecting passage on the inflow side of the stabilizing chamber and the outflow passage on the outlet side or outflow side of the stabilizing chamber include an angle, in particular an angle of approximately 90xc2x0. This makes it possible to produce radial compressors with a radially extending connecting passage between the compressor-impeller outlet edge and the stabilizing chamber and with an axial outflow passage, which extends parallel to the compressor-impeller axis, on the outlet side of the stabilizing chamber. This configuration is distinguished in particular by a compact structure. The risk of flow delamination in the subsequent outflow passage is reduced by the turbulence imparted to the flow in the stabilizing chamber.
A further feature of the compressor outflow region, which includes three different sections, is the damping of pressure pulses from the intake section of the internal combustion engine, which are damped and reduced in the relatively large volume of the stabilizing chamber. This reduces adverse effects on the compressor performance.
In one exemplary configuration, the stabilizing chamber is of cylindrical configuration, the longitudinal center axis of the stabilizing chamber extending orthogonally with respect to the longitudinal axis of the connecting passage. Due to the lateral offset between the respective axes of connecting passage and stabilizing chamber, the compressed medium flows out of the connecting passage into the lateral region of the stabilizing chamber and is diverted in circular form due to the cylindrical shape of the stabilizing chamber. In this case, the outer wall of the connecting passage may be arranged tangentially with respect to the wall of the cylindrical stabilizing chamber, so that steps in the transition from the connecting passage to the stabilizing chamber, which may produce turbulence, are avoided.
The stabilizing chamber and the outflow passage may be arranged coaxially with respect to one another, i.e., there is no need for any further diversions of the compressed medium during the transfer from the stabilizing chamber into the outflow passage. The outflow passage may in particular have a smaller cross-section than the stabilizing chamber, and an inlet contour which is favorable in terms of flow may be provided in the transition.
In a further example embodiment, the outflow passage is configured as a diffuser which has a cross-section which widens in the direction of flow, the widening angle being, e.g., less than 5xc2x0.
In a further example embodiment, the volume of the stabilizing chamber is set in a predetermined ratio to the free cross-section of flow of the connecting passage, while, e.g., a predetermined limit value in the ratio of chamber volume to passage cross-section of flow is to be exceeded.